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单词 TangentBundle
释义

tangent bundle


Let M be a differentiable manifold. Let the tangent bundle TM of M be(as a set) the disjoint unionMathworldPlanetmath mMTmM of all the tangent spacesPlanetmathPlanetmath to M, i.e., the set of pairs

{(m,x)|mM,xTmM}.

This naturally has a manifold structureMathworldPlanetmath, given as follows. For M=n, Tn is obviously isomorphicPlanetmathPlanetmathPlanetmath to 2n, and is thus obviously a manifold. By the definition of a differentiable manifold, for any mM, there is a neighborhood U of m and a diffeomorphism φ:nU. Since this map is a diffeomorphism, its derivativePlanetmathPlanetmath is an isomorphismPlanetmathPlanetmathPlanetmath at all points. Thus Tφ:Tn=2nTU is bijectiveMathworldPlanetmathPlanetmath, which endows TU with a natural structure of a differentiable manifold. Since the transition maps for M are differentiableMathworldPlanetmathPlanetmath, they are for TM as well, and TM is a differentiable manifold. In fact, the projection π:TMM forgetting the tangent vector and remembering the point, is a vector bundle. A vector field on M is simply a sectionPlanetmathPlanetmath of this bundle.

The tangent bundle is functorial in the obvious sense: If f:MN is differentiable, we get a map Tf:TMTN, defined by f on the base, and its derivative on the fibers.

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更新时间:2025/5/5 1:57:59